Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2000-01-13
2001-04-10
Langel, Wayne (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C423S651000, C423S652000, C518S704000
Reexamination Certificate
active
06214314
ABSTRACT:
This invention relates to the production of methanol. There is an increasing demand for methanol for the production of motor fuel additives such as methyl t-butyl ether (MTBE) and t-amyl methyl ether (TAME). These additives are produced as a result of the reaction of methanol with the appropriate olefin, e.g. isobutene in the case of MTBE. The relevant olefins are normally produced by cracking a suitable hydrocarbon feedstock e.g. at a refinery. Conveniently the additives are manufactured at, or adjacent to, the source, e.g. refinery, of the relevant olefins. A typical refinery may produce 2500 US barrels/day (approx. 400 m
3
/d) of MTBE for which about 110 te/day of methanol is required. Typical refinery methanol requirements are in the range 50-200 te/d. Usually the methanol is imported to the site from a methanol plant which typically produces 1500-3000 te/d.
Many processes operating at refineries require hydrogen as a reactant: while hydrogen is generally produced as a byproduct of naphtha catalytic reforming, there is often a need for further hydrogen supplies than are produced by such reforming. As a consequence many refineries also incorporate a hydrogen plant. Typical refinery hydrogen plants have a capacity in the range 50-200 te/d of hydrogen. We have realised that there are economic advantages in arranging for that hydrogen plant to be integrated with a methanol plant of sufficient size to provide the methanol required at the refinery for production of MTBE and/or TAME.
We have devised such an integrated process. Hydrogen is normally manufactured by steam reforming a hydrocarbon feedstock, such as methane, natural gas, or naphtha, at an elevated temperature and pressure producing a reformed gas stream containing hydrogen, carbon oxides, steam and methane, followed by subjecting the reformed gas stream to the shift reaction to convert carbon monoxide in the reformed gas to carbon dioxide with the production of an equivalent amount of hydrogen, and then separating the hydrogen from the shifted gas stream. The separation is often effected by an adsorption process, such as pressure swing adsorption, after condensing out the steam from the shifted gas. The waste gas, containing methane, carbon oxides and a small proportion of hydrogen, from the separation step is generally used as fuel in the steam reforming process. We have realised that if the steam is condensed from the reformed gas and then the de-watered reformed gas is subjected to a step of methanol synthesis, without any further compression, a significant amount of methanol can be produced. This methanol can be separated and then hydrogen can be separated from the residual gas, optionally after subjecting the residual gas to the shift reaction after adding steam. By this route it is possible to produce sufficient methanol to meet the refinery requirements for only a moderate increase in the size of the refinery hydrogen plant. The present invention may be used to modify an existing hydrogen plant to provide for co-production of hydrogen and methanol.
Accordingly the present invention provides a process for the co-production of hydrogen and methanol comprising
a) subjecting a hydrocarbon feedstock to steam reforming at an elevated pressure and temperature to produce a reformed gas stream containing hydrogen, carbon oxides, methane and unreacted steam;
b) cooling the reformed gas to condense steam therein and separating condensed water;
c) without further compressing the resultant de-watered reformed gas, subjecting the de-watered reformed gas to methanol synthesis and separating synthesised methanol from the product to leave an unreacted gas stream; and
d) separating hydrogen from the unreacted gas stream, optionally after adding steam to said unreacted gas and subjecting the mixture of unreacted gas and steam to the shift reaction.
Prior to steam reforming, the hydrocarbon feedstock, e.g. methane, natural gas, associated gas, or naphtha, should be desulphurised, for example by addition of a small proportion of hydrogen and passage of the mixture over a hydrodesulphurisation catalyst such as nickel or cobalt molybdate followed by absorption of hydrogen sulphide produced by the hydrodesulphurisation reaction with a suitable absorbent, especially a bed of a particulate zinc oxide or zinc carbonate composition.
The steam reforming reaction is an endothermic reaction and is normally effected by passing a mixture of the desulphurised hydrocarbon feedstock and steam through tubes containing a steam reforming catalyst, normally nickel supported on a shaped support such as rings of alumina or a calcium aluminate cement, while strongly heating the tubes. The tubes are usually heated in a furnace fuelled with a suitable hydrocarbon-containing stream; alternatively the tubes may be located within a high temperature convective heat exchange reformer, for example as described in GB 1 578 270. In this type of heat exchange reformer, the catalyst is disposed in tubes extending between a pair of tube sheets through a heat exchange zone. Reactants are fed to a zone above the upper tube sheet and pass through the tubes and into a zone beneath the lower tube sheet. The heating medium, for example the hot product of combusting a fuel with air, is passed through the zone between the two tube sheets.
As described hereinafter, whichever type of reformer is employed, the fuel used to provide the heat to heat the reformer tubes may in at least part be the waste gas remaining after separation of the desired hydrogen product. The tubes are generally heated to such an extent that the reformed gas leaves the catalyst at a temperature in the range 750-950° C., especially 800-900° C. The steam reforming reaction is operated at an elevated pressure. The pressure is generally in the range 20-50 bar abs., and preferably is in the range 25-40 bar abs.
The steam may be introduced by direct injection of steam and/or by saturation of the feedstock by contact of the latter with a stream of heated water. The amount of steam introduced is preferably such as to give a steam ratio in the range 2 to 3.5 moles of steam per gram atom of hydrocarbon carbon in the feedstock.
Before the endothermic reforming step, the hydrocarbon steam mixture may be subjected to a step of adiabatic low temperature reforming. In such a process, the hydrocarbon steam mixture is heated, typically to a temperature in the range 400-600° C., and then passed adiabatically through a bed of a suitable catalyst, usually a catalyst having a high nickel content, for example above 40% by weight. During such an adiabatic low temperature reforming step any hydrocarbons higher than methane react with steam to give a mixture of methane, carbon oxides and hydrogen. The use of such an adiabatic reforming step, commonly termed pre-reforming, is desirable to ensure that the feed to the endothermic reforming step contains no hydrocarbons higher than methane and also contains a significant amount of hydrogen. This is desirable in order to minimise the risk of carbon formation on the catalyst in the reformer tubes.
After any such pre-reforming step the feedstock/steam mixture is further heated, if necessary, to the reformer tubes inlet temperature which is typically in the range 450-600° C.
The reformed gas from the endothermic reforming step is then subjected to heat recovery, usually by steam raising to provide the process steam. Also by heat exchange, heat may be recovered from the reformed gas and/or from the gases used to heat the reformer tubes, to provide heat for heating the feedstock/steam mixture to the reformer inlet temperature and/or, where a step of pre-reforming is used, to heat the feedstock/steam mixture to the pre-reformer inlet temperature and/or to heat the pre-reformed gas to the desired inlet temperature of the reformer tubes.
After heat recovery as aforesaid from the reformed gas, the reformed gas is cooled to condense the excess of steam therein as water. The condensed water is then separated to give a de-watered reformed gas. If desired, the cooling can be effected by direct
Imperial Chemical Industries plc
Langel Wayne
Pillsbury & Winthrop LLP
LandOfFree
Process for the preparation methanol and hydrogen does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the preparation methanol and hydrogen, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation methanol and hydrogen will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2552249